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Stressing Out Yeast

Gasch et al. used gene arrays of wild-type and strains of mutant yeast lacking specific transcription factors to study how yeast genes are regulated in response to diverse environmental stimuli (changes in redox status, heat shock, hyperosmotic shock, amino acid starvation, nitrogen depletion, and progression into stationary phase). Two major clusters of genes were regulated by each of these stresses and were called the "environmental stress response" (ESR): the induced ESR cluster and the repressed ESR cluster. The ESR was not simply a response to any change in environmental conditions, but was triggered only during a stressful change. When cells that had adapted to a particular stress (heat shock or hyperosmolar conditions) returned to normal conditions, the ESR was not triggered. Interestingly, the magnitude and duration of the ESR correlated with the magnitude of the stress (higher temperatures produced a longer and stronger ESR). Finally, ESR was not due to the activation of a single transcription factor or regulatory complex, but was regulated by specific factors for each type of stress applied. Thus, there appears to be significant convergence of signaling pathways that can regulate the ESR, depending on the stress experienced. The authors also investigated the unique responses generated by each of these stresses.